#818: interface sizes are relative to the system's display scale (100% is native, Auto goes; 75-200% in Preferences, pref.uiScale takes 0.75-3, "auto" reads as 1); interface_size moved above batch_rename_dialog's doc comment; tests and docs follow

docs/mcp.md

@@ -417,12 +417,11 @@ on; `key` resolves keys the way the canvas does. Commands behind keys:
   nested layers), Escape or a click drops it.
 - `pref.reduceMotion {on?}`: reduced motion (the interface's own animations off; the system's
   accessibility setting turns it on too). Prototype transitions still play.
-- `pref.uiScale {scale?}`: how large the whole interface is drawn. `scale` is `"auto"` (the system's
-  display scale, the default) or a fixed size from 0.75 to 3 where 1 is one screen pixel per point
-  whatever scale the system reports, so a 2× screen needs 2 to match Auto. 1.25 means 125 %, not 125
-  (outside the range it stops at the nearest end). Omit `scale` to read it. The canvas zoom is separate.
-  A window too small for a fixed size draws a smaller one until it is larger; the choice is kept.
-  In the browser the interface always follows the browser's zoom.
+- `pref.uiScale {scale?}`: how large the whole interface is drawn, relative to the system's display
+  scale: 1 (the default) is the system's own size on every screen, 1.25 means 125 %, not 125; from
+  0.75 to 3 (outside the range it stops at the nearest end; `"auto"` is 1). Omit `scale` to read it.
+  The canvas zoom is separate. A window too small for a size above 100 % draws a smaller one until
+  it is larger; the choice is kept. In the browser the interface always follows the browser's zoom.
 - `pref.autoSave {on?}`: files that have a path save themselves a few seconds after they change
   (off by default; the desktop app's timer does it, so scripts still call `file.save`).
 - `pref.language {language: system|en|cs|ru|es|es-419|fr|de|pt-BR|ja|ko|zh-Hans|…}`: the app's interface language, applied live ("system":